The present invention relates to a biaxially oriented polyester film, an adhesive film and a colored hard coat film. In more retail, the present invention relates to a biaxially oriented polyester film, an adhesive film, and a colored hard coat film, which are suitable for being adhered to the display surfaces of electronic displays such as CRTs and liquid crystal display devices and then for being used.
The CRT displays and the like of televisions and personal computers emit three lights consisting of blue light, green light and red light to display images. However, the displays and the like further emit neutral color lights between the blue light and the green light and between the green light and the red light, respectively, and have caused a problem that the hue contrasts of the images have been blurred by the neutral color lights. Thereby, the solution of the problem has strongly be desired, because the states, that personal computers are watched for long times, have been increased according to the rapid popularization of the personal computers.
As a measure for the problem, it was proposed, in JP-A 11-335639 (1999) (hereinafter, JP-A means xe2x80x9cJapanese Unexamined Patent Applicationxe2x80x9d.), that carbon black was added to an adhesive layer when a protecting film comprising a protecting layer and the adhesive layer was adhered to an image display surface. The above JP-A is disclosing that the hue contrasts of images become clear, because the light absorbance of the adhesive layer is evenly increased over the each wavelength of the visible light zone due to the carbon black contained in the adhesive layer, and thereby the transmission of the neutral color lights between the blue light and the green light and between the green light and the red light, respectively, can be restrained. However, such an evenly lowering method of the transmittance, as the method in said JP-A, has a defect that the light quantity itself of a cathode-ray tube is decreased, consequently lowering the brightness of the cathode-ray tube.
As a method for solving the problem that the brightness of the cathode-ray tube is lowered, it has been proposed in JP-A 58-153904 (1983) to use color filters for giving selectivity to the transmittance of the visible light to improve the contrast and color purity. A similar method for plasma displays has been also proposed in Gekkan Display Vol. 58 (published by Techno Times Ltd., the April number, 2000), page 72 to 77. However, these color filters are not integrating-type color filters with cathode-ray tubes but attaching-type color filters to the outer surfaces. Therefore, since an air layer exists between a cathode-ray tube and an outer surface filter, there have been the defects that it is very difficult to control the reflectivity of outer light and the visibility is liable to be lowered by the outer light.
In addition, it is proposed in JP-A 57-5251 (1982) to add a pigment to the glass of a cathode-ray tube and then to use the obtained glass having selective absorption for the visible light. However, the method is now not commercialized, because the production cost of the glass is very high. Additionally, since the glass thickness of a flattened cathode-ray tube, which is being increased in recent years, is largely different between the central portion and the peripheral portions of the tube, it is extremely difficult to give uniform selective absorbability according to the addition method as described in the JP-A.
Hence, it has strongly been desired to provide an optical protection film which can be adhered to the image display surface of a CRT, a liquid crystal display device and the like to improve the contrast and color purity without lowering the brightness, in order to overcome the above-described defects. Further, for the optical protection film, the following improvements have strongly been desired; the simplification of processes, the improvement in the handleability of the adhesive layer, the improvement of transparency, the prevention in the deterioration of visibility due to outside light, the improvement of wear resistance, and the prevention in the delamination among the layers constituting the protection film, in addition to the improvement of the contrast and color purity without deteriorating the brightness of an image display device.
An object of the present invention is to provide a biaxially oriented polyester film which can solve the above-described problems and improve the contrast and the color purity without deteriorating the brightness.
Further, another object of the present invention is to provide an adhesive film which can improve the contrast and the color purity without deteriorating the brightness and further to improve delamination resistance among the layers.
Furthermore, another object of the present invention is to provide a colored hard coat film which can improve the contrast and the color purity, without deteriorating the brightness, and improve delamination resistance.
The further other objects and advantages of the present invention will be clarified by the following explanation.
According to the present invention, firstly, the above-described objects and advantages of the present invention are achieved with a biaxially oriented polyester film characterized in that
(1) said film contains a coloring matter;
(2) a haze value of said film is at most 5%;
(3) a wavelength (X) of the maximum absorption peak of light in wavelengths of 540 to 630 nm is in the range of 560 to 610 nm;
(4) a half band width of the maximum absorption peak of light in wavelengths of 540 to 630 nm is not more than 80 nm;
(5) a value (Tx/T540), obtained by dividing a light transmittance (Tx) at the wavelength (X) of the maximum absorption peak of light in wavelengths of 540 to 630 nm by a light transmittance (T540) at a wavelength of 540 nm, is less than 0.80;
(6) a value (T620/T540), obtained by dividing a light transmittance (T620) at the wavelength of 620 nm by a light transmittance (T540) at a wavelength of 540 nm, is in the range of 0.5 to 1.5;
(7) a value (T450/T540), obtained by dividing a light transmittance (T450) at the wavelength of 450 nm by a light transmittance (T540) at a wavelength of 540 nm, is in the range of 0.5 to 1.5; and
(8) said film is a base film for a colored hard coat film to be laminated to an image display surface.
According to the present invention, secondly, the above-described objects and advantages of the present invention are achieved with an adhesive film comprising the biaxially oriented polyester film of the present invention and the first adhesive layer disposed on one side of the biaxially oriented polyester film.
In addition, according to the present invention, thirdly, the above-described objects and advantages of the present invention are achieved with a colored hard coat film characterized in that
(1) said colored hard coat film comprises a transparent substrate film and a hard coat layer disposed on one side of the substrate film;
(2) said colored hard coat film contains a coloring matter;
(3) a wavelength (X) of the maximum absorption peak of light in wavelengths of 540 to 630 nm is in the range of 560 to 610 nm;
(4) a half band width of the maximum absorption peak of light in wavelengths of 540 to 630 nm is not more than 80 nm;
(5) a value (Tx/T540), obtained by dividing a light transmittance (Tx at the wavelength (X) of the maximum absorption peak of light in wavelengths of 540 to 630 nm by a light transmittance (T540) at a wavelength of 540 nm, is less than 0.80;
(6) a value (T620/T540), obtained by dividing a light transmittance (T620) at the wavelength of 620 nm by a light transmittance (T540) at a wavelength of 540 nm, is in the range of 0.5 to 1.5;
(7) a value (T450/T540), obtained by dividing a light transmittance (T450) at the wavelength of 450 nm by a light transmittance (T540) at a wavelength of 540 nm, is in the range of 0.5 to 1.5; and
(8) said colored hard coat film is a hard coat film to be laminated to an image display surface.